This invention relates generally to improvements in oil seals and related seal systems for preventing oil leakage in connection with rotating shafts, and particularly in connection with relatively high speed rotating shafts in turbomachines and the like. More specifically, this invention relates to an improvement in oil seals utilizing principles of dynamic air-oil separation to seal passage of a rotatable shaft through an end wall of a bearing housing in high misalignment applications.
In turbomachinery, a rotatable shaft is commonly supported by appropriate journal and thrust bearings mounted within a bearing housing, wherein oil is circulated from a sump to lubricate the bearings. The rotatable shaft extends through an end wall of the bearing housing, at one or both ends thereof, for appropriate connection to other components of the turbomachine, such as a turbine wheel, compressor wheel, or other suitable shaft drive means or shaft load. Examples of such turbomachines include turbochargers, turbocompressors, gas turbine engines, air turbine starter motors, and the like. Examples of Air Turbine Starters are shown in U.S. Pat. Nos. 4,871,296; 4,914,906; and 5,267,433, incorporated herein by reference.
In general terms, it is highly desirable to minimize and eliminate oil leakage along the rotating shaft and through the end wall of the bearing housing. Alternately stated, it is desirable to confine circulatory oil flow to the interior of the bearing housing. In this regard, a wide variety of oil seal configurations have been proposed in efforts to overcome oil leakage problems. However, the high speed shaft rotation and other operating conditions in a typical turbomachine environment have generally precluded complete elimination of the oil leakage. That is, high speed shaft rotation tends to result in relatively rapid wear of seal structures and early onset of oil leakage. This problem is compounded by high temperature operating environments.
Honeywell International, Inc. is well known as a world leader in aerospace equipment that has non-contacting clearance seals, such as those disclosed in U.S. Pat. Nos. 5,538,258 (xe2x80x9cOil Seal for a High Speed Rotating Shaft;xe2x80x9d Hager, J.; Geck, K.; Giesler, W.; Farnsworth, G.) and 5,636,848 (xe2x80x9cOil Seal for a High Speed Rotating Shaft;xe2x80x9d Hager, J.; Geck, K.; Giesler, W.; Mathis, D.), incorporated herein by reference. These patents show proven designs that provide a reliable oil to air seal for the output section of an Air Turbine Starter (ATS). These systems incorporate a slinger rotor mounted on the shaft for rotation therewith and located inboard of the end wall of the bearing housing. The slinger rotor and the end wall of the bearing housing are designed to provide at least one and preferably multiple dynamic air-oil separator structures for centrifugal pumping of oil, so as to keep the oil away from the shaft passage in the end wall of the bearing housing.
The clearance seals disclosed in these patents, however, have traditionally been used with ATS systems with sprag clutch output sections. In such applications, the bearing support system provides excellent rotating shaft alignment to the seal housing (stator). In applications with other clutch types, for example pawl and ratchet clutch systems, the bearing support system has a tolerance build-up that can vary the shaft alignment, for example up to 0.3 degrees to the seal housing.
When such shaft misalignment occurs, the gap between the seal rotor and housing opens and closes as the seal rotor rotates through 360xc2x0 with each rotation. This opening and closing action can produce a negative pumping action that negates the positive pumping action of the dynamic air-oil separator structures of the oil seal, thereby negating the effective operation of the clearance seal.
The clearance seals disclosed in the above-stated patents have thus far not provided adequate sealing of output shafts on air turbine starters using pawl and ratchet clutches. There exists, therefore, a continuing need for further improvements in oil seal structures for use in turbomachines and the like, for substantially eliminating oil leakage through the end wall of a bearing housing, notwithstanding high speed shaft rotation and high temperature operating conditions in high misalignment applications. The present invention fulfills these needs and provides further related advantages. The present invention also provides additional improvements to the dynamic air-oil separator structures used in non-contact clearance seal applications.
In accordance with the invention, an improved slinger rotor for an improved oil seal is provided for reducing negative pumping action caused by the opening and closing of the gap between the seal rotor and housing as the shaft rotates through 360xc2x0 in high misalignment applications. The invention is particularly suited for use in association with dynamic air-oil separator structures of an oil seal for substantially eliminating oil leakage along a possibly misaligned rotatable shaft extending through a shaft passage formed in an end wall of a bearing housing in a turbomachine or the like, including, for example, ATS applications with ratchet and pawl clutch assemblies. The invention may also be used with other types of clutch assemblies, e.g., sprag clutch assemblies, and flyweight actuated clutch assemblies such as described in U.S. Pat. No. 5,419,420, incorporated herein by reference. The improved rotor and oil seal includes a slinger rotor mounted within the bearing housing, at the inboard side of the end wall of the bearing housing.
In one embodiment, the slinger rotor has a radially outward extending slinger ring with an outboard seal face which faces the inboard end of the end wall of a bearing housing. The seal face has radially oriented slots and a circumferential groove or grooves. During rotation of the slinger rotor, the radially oriented slots, combined with circumferential grooves, draw oil away from the area in between the seal face of the slinger ring and the inboard side of the end wall of the bearing housing. In this area, the negative pumping action has traditionally saturated the seal and caused leakage in high misalignment applications. The circumferential grooves also reduce air pumping at the face by allowing air to flow circumferentially to match the nutation (or oscillatory movement) of the rotor.
In another aspect of the invention, the slinger rotor defines an internal bore with axially extending lands sized for press-fit mounting onto the rotatable shaft. The lands at the outboard end of the bore are separated by slots which define additional centrifuge surfaces. During shaft rotation, oil and air within these slots is pumped by centrifugal action in a direction away from the end wall. An axial end face on the slinger rotor, opposite the end wall of the bearing housing (i.e., the inboard end), includes radially open notches which function as slinger ports to discharge the pumped oil to the interior of the bearing housing.
Other features and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.